1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk.
2. Description of the Related Art
As tape-form magnetic recording media for audio, video, and computers, and disc-form magnetic recording media such as flexible discs, a magnetic recording medium has been used in which a magnetic layer having dispersed in a binder a ferromagnetic powder such as γ-iron oxide, Co-containing iron oxide, chromium oxide, or a ferromagnetic metal powder is provided on a support. With regard to the support of the magnetic recording medium, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc. are generally used. Since these supports are drawn and are highly crystallized, their mechanical strength is high and their solvent resistance is excellent.
The magnetic layer, which is obtained by coating the support with a coating solution having the ferromagnetic powder dispersed in the binder, has a high degree of packing of the ferromagnetic powder, low elongation at break, and is brittle, and it is therefore easily destroyed by the application of mechanical force and might peel off from the support. In order to prevent this, an undercoat layer is provided on the support so as to make the magnetic layer adhere strongly to the support.
On the other hand, magnetic recording media are known in which a radiation-cured layer is formed using a compound having a functional group that is cured by radiation such as an electron beam, that is, a radiation curing compound. These radiation-cured layers formed from the radiation curing compound give a magnetic layer having insufficient smoothness, and adequate electromagnetic conversion characteristics cannot be obtained (ref. JP-A-60-133531, JP-A-57-40747, and JP-A-2001-84582; JP-A denotes a Japanese unexamined patent application publication). Furthermore, since the peel-off strength of the magnetic layer is insufficient, when such a magnetic recording medium is run repeatedly in a VTR, etc., a part of the magnetic layer peels off, thus giving rise to the problem of faults such as dropouts. Moreover, since the radiation-cured layer is soft, the problem of it sticking to guide rollers, etc. during a coating step, etc. often occurs.
Furthermore, a magnetic recording medium provided with a radiation-cured layer having a cyclic structure has been proposed (ref. JP-A-2003-132522). However, there is a desire for a further improvement in durability, particularly of a magnetic recording medium employing fine particles as a magnetic substance.